Two-step Thermochemical Cycle Research Articles

Light-assisted thermochemical reduction of CuFe2O4 within a photo-thermogravimetric analyser for solar fuel production

The solar thermochemical cycle has emerged as a promising clean energy technology that enables the splitting of water for solar fuel production. However, conventional two-step thermochemical cycles using single-metal oxides require high operating temperatures above 1000 °C, especially for the reduction step. Typical solar thermal systems struggle to meet such high temperature requirements, making it vital to reduce the operating temperature. To find a solution enabling lower temperature requirements, we propose a photo-thermochemical reduction (PTR) strategy, which employs light illumination as assistance, combining both thermally induced and photo-induced effects for more generation of oxygen vacancies (VOs), within the oxygen carrier copper ferrite (CuFe2O4). Experimental studies were performed in a specially-designed photo-thermogravimetric analyser (photo-TGA) that directly measures the weight change of solid reactants under direct light illumination. The results indicate that the PTR achieves a decrease of nearly 40 °C in temperature requirements, giving a higher oxygen release of 21% compared to that driven by pure thermal heating at 800 °C. We also measured an increase of 0.09 in the non-stoichiometry parameter δ in the photo-TGA. Additionally, we observed that oxygen release increases distinctly with the light intensity of incident illumination. From the viewpoint of spectral ranges, ultraviolet and visible light illumination give the primary boost to the generation of photo-induced VOs. These results demonstrate the effective assistance of concentrated solar energy to enhance the two-step thermochemical cycle for solar fuel production at lower temperatures.

The study of CO2 splitting kinetics on LSM perovskite oxides in the solar-driven two-step thermochemical cycle

La0.6Sr0.4MnO3 (LSM) has seen enormous interest since they were proposed for the two-step thermochemical cycle (TSTC). However, its oxidation kinetics is notably deficient, and few studies have been documented. In this work, the reactivity activity relaxation (RAR) and electrical conductivity relaxation (ECR) methods are used to investigate the reaction kinetics of CO2 splitting by LSM oxidation. The results of RAR test show that the Sestak-Berggren model is the most precise depiction of the reaction mechanism, and the apparent kinetic parameters are obtained. In addition, the chemical bulk diffusion coefficient and the oxygen surface exchange coefficient of the reactions are obtained using the ECR method. It’s found that the surface reaction process is the rate-limiting step of the whole oxidation reaction process. In conclusion, this study examines in detail the kinetic properties of LSM oxidation reaction and provides a reference for its application in TSTC.

A review of solar thermochemical cycles for fuel production

Solar-driven CO2/H2O splitting via a two-step solar thermochemical cycle is a promising approach for fuel production and carbon neutrality to address the intermittent instability and low energy density of solar energy while taking advantage of its clean and nonpolluting nature. However, current experimental efficiencies are still below theoretical levels due to various limitations such as material properties and energy loss occurring in the reactor. The reactor, as an important component for commercialization, still faces various challenges including high reaction temperature, limited reactor material longevity, high temperature sealing of moving parts, and slow adsorption and desorption rate of porous structure lining. This paper reviews researches on solar thermochemical oxygen carriers and related reactors, with particular focus on analyzing reactor design criteria, modeling methods, energy efficiency and energy loss analysis. In addition, obtaining low partial pressure oxygen for reduction reactions, heat recovery methods, and synergies between the reactor and solar concentrating system play a significant role in further improving energy efficiency. This work demonstrates the feasibility of two-step solar thermochemical cycles in renewable energy technologies and provides guidance for future innovations in this field.

Multi-field coupling and collaborative optimization design of the solar thermochemical cycle process based on ceria

Most solar reactors commonly encounter challenges such as high-temperature gradients, suboptimal photo-thermal efficiency, and limited catalyst utilization. This lack of coordination in the design of solar reactors stems from the inadequate integration of the photothermal-chemical coupling synergistic relationship within the reactor. We developed a comprehensive multi-physics coupling mathematical model that incorporates optics, heat transfer, and chemical reactions to facilitate the cooperative optimization design of solar reactors. This study unveils the multi-field coordination mechanism within solar reactors. The optimization design of the secondary concentrator, reactor structure, fluid flow layout, and porous media catalyst structure was systematically carried out. A two-step thermochemical cycle of methane reducing cerium oxide decomposing water vapor to produce hydrogen was used as the reaction system to analyze the performance of the prototype reactor. The influences of ray power, reaction flow rate, and oxygen carrier mass on the solar-to-chemical efficiency were analyzed. The optimization results demonstrate that, by considering factors such as light power, mass transfer flow, and oxygen carrier mass within the optimization framework, the solar chemical energy conversion efficiency can reach a maximum of 38.75%.

Redox Performance and Optimization of the Chemical Composition of Lanthanum–Strontium–Manganese-Based Perovskite Oxide for Two-Step Thermochemical CO2 Splitting

The effects of substitution at the A- and B sites on the redox performance of a series of lanthanum–strontium–manganese (LSM)-based perovskite oxides (Z = Ni, Co, and Mg) were studied for application in a two-step thermochemical CO2 splitting cycle to produce liquid fuel from synthesis gas using concentrated solar radiation as the proposed energy source and CO2 recovered from the atmosphere as the prospective chemical source. The redox reactivity, stoichiometry of oxygen/CO production, and optimum chemical composition of Ni-, Co-, and Mg-substituted LSM perovskites were investigated to enhance oxygen/CO productivity. Furthermore, the long-term thermal stabilities and thermochemical repeatabilities of the oxides were evaluated and compared with previous data. The valence changes in the constituent ionic species of the perovskite oxides were studied and evaluated by X-ray photoelectron spectroscopy (XPS) for each step of the thermochemical cycle. From the perspectives of high redox reactivity, stoichiometric oxygen/CO production, and thermally stable repeatability in long-term thermochemical cycling, Ni0.20-, Co0.35-, and Mg0.125-substituted La0.7Sr0.3Mn perovskite oxides are the most promising materials among the LSM perovskite oxides for two-step thermochemical CO2 splitting, showing CO productivities of 387–533 μmol/g and time-averaged CO productivities of 12.9–18.0 μmol/(min·g) compared with those of LSM perovskites reported in the literature.

Chemical kinetics of two-step thermochemical decomposition of hydrogen sulfide over nickel sulfide

The study develops a multistep reaction mechanism for a two-step thermochemical cycle that produces hydrogen from H2S decomposition, using nickel sulfide as a catalyst. Two mechanisms were investigated: 1) a gas-phase mechanism that occurs without a Ni catalyst to determine the contribution of thermal decomposition to the overall reaction without a catalyst, and 2) a microkinetic model of the catalytic Ni surface phase to examine the key parameters affecting the overall cycling process and H2S conversion efficiency. Both mechanisms were validated using CHEMKIN-Pro software to analyze the experimental data and trends. The study showed that gas-phase H2S conversion was not kinetically significant below 850 °C. The microkinetic model showed that most H2S was transformed into H2 and NiS products when the sulfurization temperature reached 500 °C. Additionally, the site fraction of NiS decreased while the number of free active nickel sites increased as the regeneration temperature increased from 500 °C to 800 °C. A temperature limit of 700 °C was set for the regeneration step due to the agglomeration behavior of nickel sulfide particles.

Physical system behavior and energy flow analysis of a solar driven hydrogen production plant based on two-step thermochemical redox cycles

Two-step thermochemical water splitting using concentrated solar power offers promising potential for green hydrogen production as a part of a future sustainable energy economy. In this study, a system and energy flow analysis of a large scale 250 kW reactor prototype is presented by using a complex 3D-simulation model. Thus, the physical dynamic system behavior and potential efficiency improvements are discussed with respect to plant design and operational strategy. Regarding the plant design, different kind of heat losses as well as the influence of reactor design parameters and material modifications are analyzed. Regarding the operational strategy, crucial control parameters as cycle durations, temperatures, and mass flow rates are varied in a broad range and analyzed with respect to plant efficiency. By comparing commonly used operational strategies, the temperature swing operation turns out to be by far more efficient than any isothermal or near-isothermal operation for the current plant concept.

Analysis of cascade and hybrid processes for hydrogen production by full spectrum solar energy utilization

Hydrogen energy is a clean energy that is expected to replace fossil energy. However, current hydrogen production methods still have some drawbacks, including environmental pollution and low efficiency of photovoltaic (PV) cells at high temperature, etc., thus the current task is to explore a green and efficient hydrogen production approach. Based on spectral splitting technology, this paper proposes a hydrogen production system that combines a two-step thermochemical cycle (TC) with photovoltaic power generation electrolysis water for the first time, achieving full spectrum and efficient utilization of solar energy. The input of this system only includes solar energy and water. The high-temperature steam that is not reacted in the TC is further electrolyzed in solid oxide electrolytic cells (SOEC) directly, achieving zero carbon hydrogen production and cascade utilization of energy. A hydrogen production model for the new system is established, and the thermodynamic performance of the proposed system is evaluated. The performance of the system under different splitting wavelengths and temperatures is given and analyzed. The results show that although there is no heat recovery, the exergy efficiency of the proposed system can reach approximately 32%, and the solar-to-hydrogen (STH) efficiency can reach nearly 40% (TH=1500 °C, TL = 900 °C). Compared to TC and photovoltaic electrolysis under the same conditions, the energy utilization efficiency of the proposed system has been greatly improved, thus providing a new concept for green and efficient hydrogen production.

Thermochemical Activity of Single- and Dual-Phase Oxide Compounds Based on Ceria, Ferrites, and Perovskites for Two-Step Synthetic Fuel Production.

This study focuses on the generation of solar thermochemical fuel (hydrogen, syngas) from CO2 and H2O molecules via two-step thermochemical cycles involving intermediate oxygen-carrier redox materials. Different classes of redox-active compounds based on ferrite, fluorite, and perovskite oxide structures are investigated, including their synthesis and characterization associated with experimental performance assessment in two-step redox cycles. Their redox activity is investigated by focusing on their ability to perform the splitting of CO2 during thermochemical cycles while quantifying fuel yields, production rates, and performance stability. The shaping of materials as reticulated foam structures is then evaluated to highlight the effect of morphology on reactivity. A series of single-phase materials including spinel ferrite, fluorite, and perovskite formulations are first investigated and compared to state-of-the-art materials. NiFe2O4 foam exhibits a CO2-splitting activity similar to its powder analog after reduction at 1400 °C, surpassing the performance of ceria but with much slower oxidation kinetics. On the other hand, although identified as high-performing materials in other studies, Ce0.9Fe0.1O2, Ca0.5Ce0.5MnO3, Ce0.2Sr1.8MnO4, and Sm0.6Ca0.4Mn0.8Al0.2O3 are not found to be attractive candidates in this work (compared with La0.5Sr0.5Mn0.9Mg0.1O3). In the second part, characterizations and performance evaluation of dual-phase materials (ceria/ferrite and ceria/perovskite composites) are performed and compared to single-phase materials to assess a potential synergistic effect on fuel production. The ceria/ferrite composite does not provide any enhanced redox activity. In contrast, ceria/perovskite dual-phase compounds in the form of powders and foams are found to enhance the CO2-splitting performance compared to ceria.

A novel high-efficiency solar thermochemical cycle for fuel production based on chemical-looping cycle oxygen removal

Solar-driven two-step thermochemical cycling is a promising means to convert solar energy into storable and transportable chemical fuel, in which hydrogen or carbon monoxide is generated by continuous reduction and oxidation reactions. However, the high energy consumption of deoxygenation in the reduction step is an important factor restricting its efficiency improvement. In this work, we propose a fuel production system with thermochemical cycles coupled with chemical-looping cycles, which uses the chemical-looping cycle oxidation reaction at relatively low temperature to absorb the oxygen produced by the thermochemical cycle reduction reaction. The oxygen-carriers in the chemical-looping cycle can be reduced by adding reductants or direct heating with waste heat from the thermochemical cycle. The coupled system can remove the oxygen in the thermochemical cycle reduction reaction and reduce the energy consumption in this process. In addition to the hydrogen production, waste heat from the thermochemical cycle can also be used in the chemical-looping cycle to generate extra electricity. Theoretical calculation results show that in the oxidation temperature range of 900–1100 °C, the energy consumption for separating oxygen from inert gas after sweeping in the traditional thermochemical cycle accounts for 30–57% of the total energy consumption, while the chemical-looping cycle part in the coupled system accounts for 26–36%. The coupled system can improve the solar-to-fuel efficiency by 45.9% to 20.9% and improve the solar-to-electricity efficiency by 104.1% to 14.6% without heat recovery compared to traditional thermochemical cycles when the reduction temperature is 1500 °C. Under the conditions of 20% solid-state heat recovery and 90% gas-state heat recovery, the coupled system achieves a solar-to-fuel efficiency of 28.1%. In addition, we also put forward a vacuum pump, inert gas and chemical-looping cycles combined oxygen removal method. Since the vacuum pump has high efficiency and fast deoxygenation speed in the low vacuum interval, the system efficiency can be further improved. Our research can provide a new solution to the high energy consumption of deoxygenation in thermochemical cycles.

Formation of Ba3Nb0.75Mn2.25O9-6H during thermo-chemical reduction of Ba4NbMn3O12-12R.

The resurgence of inter-est in hydrogen-related technologies has stimulated new studies aimed at advancing lesser-developed water-splitting processes, such as solar thermochemical hydrogen production (STCH). Progress in STCH has been largely hindered by a lack of new materials able to efficiently split water at a rate comparable to ceria under identical experimental conditions. BaCe0.25Mn0.75O3 (BCM) recently demonstrated enhanced hydrogen production over ceria and has the potential to further our understanding of two-step thermochemical cycles. A significant feature of the 12R hexa-gonal perovskite structure of BCM is the tendency to, in part, form a 6H polytype at high temperatures and reducing environments (i.e., during the first step of the thermochemical cycle), which may serve to mitigate degradation of the complex oxide. An analogous compound, namely BaNb0.25Mn0.75O3 (BNM) with a 12R structure was synthesized and displays nearly complete conversion to the 6H structure under identical reaction conditions as BCM. The structure of the BNM-6H polytype was determined from Rietveld refinement of synchrotron powder X-ray diffraction data and is presented within the context of the previously established BCM-6H structure.

Selection of iron-based oxygen carriers for two-step solar thermochemical splitting of carbon dioxide

The two-step solar thermochemical cycle is a prospective clean energy technology that enables the direct splitting of water and carbon dioxide for solar fuel production. However, immature oxygen carriers fundamentally restrict the solar-to-fuel conversion efficiency and thus prevent this technology from immediate industrial uptake. Focusing on the conventional iron-based oxygen carriers, this study intends to find a modified oxygen carrier with low reaction temperature requirements and excellent reaction performance, so as to attain dual optimization in terms of thermal efficiency and chemical efficiency. The thermochemical reaction characteristics of six common ferrites and four metal dopants are compared via thermogravimetric analysis under the same programmed temperature control. For further practical applications of the selected oxygen carrier, a foam-structured material with SiC as support is prepared and subsequently experimented in a self-designed 18-kW thermochemical system. The results indicate that the modified oxygen carriers obtained by direct doping of CoFe2O4 with 50wt% NiO exhibit optimal reaction performance, giving the highest CO yield of 439μmol/g. Additionally, the foam-structured material enable a peak CO yield of 7.0 mL min−1 g−1 and CO2 conversion of 45.5% at a reduction temperature of only 1100°C, which might be attributed to the micron-scale pore structure as well as the generation of aluminosilicate crystal structures.

Redox Cycles, Active Materials, and Reactors Applied to Water and Carbon Dioxide Splitting for Solar Thermochemical Fuel Production: A Review

The solar thermochemical two-step splitting of H2O and CO2 based on metal oxide compounds is a promising path for clean and efficient generation of hydrogen and renewable synthetic fuels. The two-step process is based on the endothermic solar thermal reduction of a metal oxide releasing O2 using a high-temperature concentrated solar heat source, followed by the exothermic oxidation of the reduced oxide with H2O and/or CO2 to generate pure H2 and/or CO. This pathway relates to one of the emerging and most promising processes for solar thermochemical fuel production encompassing green H2 and the recycling/valorization of anthropogenic greenhouse gas emissions. It represents an efficient route for solar energy conversion and storage into renewable and dispatchable fuels, by directly converting the whole solar spectrum using heat delivered by concentrating systems. This eliminates the need for photocatalysts or intermediate electricity production, thus bypassing the main limitations of the low-efficient photochemical and electrochemical routes currently seen as the main green methods for solar fuel production. In this context, among the relevant potential redox materials, thermochemical cycles based on volatile and non-volatile metal oxides are particularly attractive. Most redox pairs in two-step cycles proceed with a phase change (solid-to-gas or solid-to-liquid) during the reduction step, which can be avoided by using non-stoichiometric oxides (chiefly, spinel, fluorite, or perovskite-structured materials) through the creation of oxygen vacancies in the lattice. The oxygen sub-stoichiometry determines the oxygen exchange capacity, thus determining the fuel production output per mass of redox-active material. This paper provides an overview of the most advanced cycles involving ZnO/Zn, SnO2/SnO, Fe3O4/FeO, ferrites, ceria, and perovskites redox systems by focusing on their ability to perform H2O and CO2 splitting during two-step thermochemical cycles with high fuel production yields, rapid reaction rates, and performance stability. Furthermore, the possible routes for redox-active material integration and processing in various solar reactor technologies are also described.

Thermochemical Properties of High Entropy Oxides Used as Redox-Active Materials in Two-Step Solar Fuel Production Cycles

The main challenges and obstacles to the development of hydrogen/carbon monoxide production from the splitting of water/carbon dioxide through two-step solar thermochemical cycles are strongly related to material concerns. Ineed, ceria is the main benchmark redox material used in such processes because it provides very good oxidation reaction kinetics, reactions reversibility and thermal cycling stability. This is at the expense of a low reduction yield (non-stoichiometry δ in CeO2-δ) at relatively high temperatures (≥1400 °C), which requires operation at low oxygen partial pressures during the reduction step. Hence, the specific fuel output per mass of redox material, i.e., the amount of H2/CO produced per cycle, remains low, thereby limiting the overall solar-to-fuel conversion efficiency. Perovskites offer larger amounts of fuel produced per cycle but the reaction kinetics are slow. This study addresses the thermochemical investigation of a new class of metal oxides, namely high entropy oxides (HEOs), with the aim of improving the specific amount of fuel generated per cycle with good kinetic rates. Different formulations of high entropy oxides were investigated and compared using thermogravimetric analysis to evaluate their redox activity and ability to split CO2 during thermochemical cycles. Among the different formulations tested, five HEOs yielded CO with a maximum specific fuel output of 154 µmol/g per cycle. These materials’ performances exceeded the production yields of ceria under similar conditions but are still far from the production yields reached with lanthanum–manganese perovskites. This new class of materials, however, opens a wide path for research into new formulations of redox-active catalysts comparing favorably with the ceria redox performance for solar thermochemical synthetic fuel production.

Thermodynamic assessment of nonstoichiometric oxides for solar thermochemical fuel production

Two-step solar thermochemical cycling (STC) based on nonstoichiometric oxides is an ideal means of solar fuel (e.g., H2, CO) production. Screening of nonstoichiometric oxides with excellent thermodynamic performance is key to achieving high solar-to-fuel efficiency. However, application-driven materials assessment intended for reactor-level solar fuel production performance requires mimicking realistic operating conditions of on-sun tests in a laboratory setting, which makes oxides assessment and screening an onerous task to accomplish experimentally. In this work, a rapid assessment and screening model of nonstoichiometric oxides for two-step solar thermochemical cycling assuming fixed-bed flow pattern and quasi-equilibration of the solid with the flowing gas phase is developed, with solar-to-fuel efficiency being the target function of optimization. The model accounts for the thermodynamic parameters of oxide materials and typical operating conditions of experimental thermochemical cycling. This study employed the model to explore and compare two groups of typical nonstoichiometric oxides (CeO2- and (LaSr)MnO3-based) for their maximum efficiency under their uniquely optimized cycling conditions. The results show that CeO2 can reach a maximum efficiency of 12.9% at reduction temperature of 1500 °C, which is superior to other candidate materials, including 20 mol% Zr-doped CeO2 (10.1%), La0.6Sr0.4MnO3 (2.5%) and La0.8Sr0.2MnO3 (3.3%). Even when the reduction temperature is lowered to 1350 °C, ceria yields the highest efficiency amongst the candidate STC materials considered. The optimal cycling strategy depends on the inherent thermodynamic properties of the oxides. This approach serves as a framework for assessing the maximum efficiency and optimal conditions of candidate thermochemical materials within a range of constraints rather than comparing materials under arbitrary cycling conditions, which may inherently favor one material over another. For oxidation temperatures below 800–1000 °C, the model could be further improved by considering reaction kinetics.

Solar-driven H2O/CO2 conversion to fuels via two-step electro-thermochemical cycle in a solid oxide electrochemical cell

H2O/CO2 splitting via two-step solar thermochemical cycles performed with metal oxides is a promising path for fuel production. However, currently the reduction temperature of two-step thermochemical cycles is still too high and the fuel productivity is relatively low, which significantly hinders the improvement of solar-to-fuel efficiency. In this work, a two-step electro-thermochemical cycle integrated with a solid oxide electrolysis cell (SOEC) is proposed to overcome the challenges faced by two-step thermochemical cycle. Meanwhile, the definition, classification and operating mode of this cycle are expounded in detail. Additionally, a thermodynamic model of electro-assisted reduction thermochemical cycle (ERTC) for CO2 splitting is established and applied to investigate the effect of voltage (E), reduction temperature (Tred), oxygen pressure (pO2), heat recovery of the solid and gas phases on solar-to-fuel efficiency. The efficiency increases from 0.29 to 0.40 as E increases from 0 V to 0.6 V due to the required Tred of ceria could be reduced from 1500℃ to 1000℃, with pO2 = 10−6 bar. Moreover, the oxygen carrier in SOEC could even be reduced in air instead of a low-pO2 atmosphere while maintaining high efficiency. The technological challenges of high Tred and the oxygen carriers’ high sensitivity to pO2 can be mitigated in this innovative path.

Optimizing the operational strategy of a solar-driven reactor for thermochemical hydrogen production

In this paper the operational strategy of a pilot plant for regenerative hydrogen production based on two-step thermochemical redox cycles is investigated with focus on optimal operational parameters for highest solar-to-fuel efficiency. The current plant consists of a solar driven large-scale 250 kW thermochemical inert gas reactor using ceria as reactive material for water splitting and an efficient fluid heat recovery system. Here we analyse the most important process conditions, which are operating temperatures, mass flow rates and duration times for both steps in the cycle. A highly accurate and detailed simulation model combined with well-suited optimization routines reveals new insights in most efficient operational strategies. Within the optimization material and technical limits of the used components are considered, thereby yielding reliable practical results. Optimal operational parameters are found by using a temperature swing strategy with corresponding solar-to-fuel plant efficiency determined by up to 1.1%.

Holistic energy flow analysis of a solar driven thermo-chemical reactor set-up for sustainable hydrogen production

In this contribution, a holistic energy flow analysis of a solar driven pilot plant for green hydrogen production using two-step thermochemical cerium-based redox cycles is carried out. The plant consists of a heliostat field, a large-scale inert gas reactor, an efficient fluid heat recovery system and an electrical vaporizer for steam generation. The system behaviour is physically described, and energy flows are quantified using a complex simulation model considering material and geometric properties of the complete system design. The system energy flow and corresponding impact on plant efficiency is thoroughly analysed with emphasis on plant design, operational strategy, and influence of the crucial control parameters. Influences of a heat recovery system and the size of various types of heat losses are investigated, potential efficiency improvements are revealed and useful possibilities for plant design and material modifications are discussed. The transient system behaviour is investigated by varying temperatures and mass flow rates in a broad practicable range to gain more insight in efficient reactor design and plant control. Two temperature swing strategies are investigated in more detail, which are by far more efficient than any near-isothermal or isothermal strategy for this application.

Thermodynamic and First-principles Assessments of Materials for Solar-driven CO2 Splitting Using Two-step Thermochemical Cycles

Thermodynamic and First-principles Assessments of Materials for Solar-driven CO₂ Splitting Using Two-step Thermochemical Cycles

Hydrogen production by thermochemical water splitting with La0.8Al0.2MeO3-δ (Me= Fe, Co, Ni and Cu) perovskites prepared under controlled pH

Aluminum based perovskites, La0.8Al0.2MeO3-δ (Me = Co, Ni, Fe, Cu), were synthesized following the Pechini method at different pHs and evaluated for hydrogen production by water splitting in a two-step thermochemical cycle. The pH of the synthesis medium showed a critical influence in the redox properties of the aluminum-based perovskites during the thermochemical cycle. Both the thermal reduction and the hydrolysis step produce irreversible changes in the crystalline structure of La0.8Al0.2MeO3-δ perovskites prepared at acid pH, avoiding the cyclability of the material and a stable production of hydrogen during consecutive cycles. However, these changes are not observed when the perovskites were synthesized at basic pH and operated at isothermal conditions at 800 ºC. In this case, the materials keep the crystalline structure leading to stable hydrogen production during consecutive cycles. Among all the studied materials, the nickel-based La0.8Al0.2NiO3-δ perovskites exhibited the best hydrogen productivity per cycle, 4.4 cm3 STP /gmaterial·cycle (Standard Temperature and Pressure conditions), which is a remarkable result considering that the thermochemical water splitting is conducted under isothermal conditions at just 800 ºC. Moreover, this result is accompanied with a good performance of the perovskite in terms of solar to fuel efficiency (being 0.46 the ratio between the potential energy recovery from the produced hydrogen and the solar heat required for its production), comparable or even higher than values reported in the literature for other metal oxides. These results confirm the La0.8Al0.2NiO3-δ perovskite as an auspicious material for a full-scale H2 production from water splitting by solar-driven thermochemical cycles at low temperatures.